1. Field of the Invention
This invention relates to a solid image-pickup assembly particularly suitable for use in medical and industrial electronic endoscopes.
2. Description of the Prior Art
Electronic endoscopes generally have a solid image pickup device or imager such as a CCD fitted in the tip end of an insert portion to be introduced into a body. The solid image pickup device is usually supplied in the form of a solid image pickup assembly which has the image pickup device mounted on a wiring substrate and received in a package with a transparent protective glass window for transmission of incident light. The solid image pickup assembly is fixedly mounted in an objective lens barrel. The wiring substrate for mounting the solid image pickup device is flat in shape and has predetermined wiring patterns formed thereon. The wiring portions on the substrate are connected with the electrode portions on the surface of the solid image pickup device by wire bonding means.
In the case of a bronchoscope to be inserted into the bronchus, for example, its insert portion is required to be as small as possible in diameter and to contain a rigid portion of as small a length as possible. In order to meet these requirements, the solid image pickup assembly to be incorporated into the insert portion has to be small enough in size. Recently, there have been developed solid image pickup devices which are markedly improved in the degree of integration, more specifically, which are formed with ten thousands to hundred thousands picture elements on an extremely small chip of about 1-2 mm. The use of such a small device should contribute to the reduction in size of the solid image pickup assembly.
However, as mentioned hereinbefore, the actual use of a small-size solid image pickup device does not necessarily result in a corresponding reduction in size of the solid image pickup assembly as a whole, which has a triple-layer construction including a wiring substrate, a solid image pickup device mounted on the wiring substrate and protective glass covering the light receiving surface of the image pickup device. In addition, the electrodes which are formed on the front side of the solid image pickup device have to be connected to the electrodes on the wiring substrate by wire bonding means through interconnecting wires which are projected in an arch-like fashion. Therefore, it is necessary to provide a clearance of a certain width between the light receiving surface of the solid image pickup device and the protective glass. This results in an increased thickness of the solid image pickup assembly as a whole, making it difficult to shorten the length of the rigid portion at the tip end of the insert portion. Besides, the wire bonding itself requires to extend the interconnecting wires over a certain distance in a direction parallel with the face of the image pickup device, barring the reduction of the wiring substrate dimensions as well as the reduction of the diameter of the insert portion.